Objectives: To understand mechanism of opioid receptor signal transduction and cellular regulation of the receptor activities, we will identify mu opioid receptor associated proteins effecting the receptor signal trafficking and study their role in modulating the receptor function. Specific Aims: 1) to search for mu opioid receptor associated proteins by using its carboxyl tail or whole receptor as baits; 2) to identify mu opioid receptor regulatory proteins, and the motif of interaction between mu opioid receptor and these regulatory proteins; 3) to investigate the role of these regulatory proteins in mu opioid receptor function. To achieve the proposed goals, molecular cloning techniques such as fusion protein construction, site-directed mutagenesis will be used. In particular, yeast two-hybrid system will be carried out for identifying the interaction between mu opioid receptor associated proteins and the receptor.